Article of resin bonded abrasive grains



Patented Jan. 19, 1945 ARTICLE OF nssm BONDED ABRASIVE cams Carl E.Barnes, Cambridge, Mass, assignor to Norton Company, Worcester, Mass, acorporation of Massachusett No Drawing. Application August 25, 1941,Serial No. 408,195

Claims.

This invention relates to abrasive articles and more particularly toarticles made of abrasive grains bonded by a resin formed of polymerizedunsaturated methylene compounds.

Methyl methacrylate and similar polymerizable substances will serve as abond for abrasive grains; but for various abrasive purposes, they haveundesired characteristics, such as being not hard or strong enough orhaving too low a softening point or flowing too readily or smearing overthe face of a grinding wheel when used in a dry grinding operation.

One object of my invention is to provide an improved abrasive article,such as a grinding wheel, which is made of abrasive grains bonded bypolymerized unsaturated methylene compounds and which has a suitablehardness. strength, resistance to heat or other required physicalcharacteristics.

Methyl methacrylate in its monomeric form contains the polymerizableunsaturated group CH2=C-, and it is considered to polymerize by arearrangement of the primary valence bonds in such a way as to formlinear chains having the group CH2C-- as a repeating unit. The

linear chain type or ester may be interpolymerized with a furtherpolymerizable compound containing two of the unsaturated CH2: groupswhich are independently polymerizable. During polymerization the growingchains incorporate the CH2 groups of both substances and form aninterpolymer having a three dimensional structure which is harder or hasa higher resistance to heat or is less soluble or shows other differentcharacteristics.

I have found that the vinyl and isopropenyl acrylates, chloracrylatesand methacrylates, which have two of the unsaturated methylene groups,may be used to cross link various linear chain types of base substances,such as methyl methacrylate, to form interpolymers which serve as usefulbonds for abrasive grains.

A further object of the invention is, therefore, to provide abrasivearticles which comprise such interpolymerized substances and to form aSeries of abrasive bodies of widely different characteristics which willserve many useful purposes. Further objects will be apparent in thefollowing disclosure.

In accordance with this invention, I propose to make various types oiabrasive articles, such as grinding wheels, sharpening stones,cutting-off wheels and honing, lapping and polishing detalline alumina,silicon carbide, boron carbide,

diamonds and other types of abrasive material, with resin substancesformed of copolymers of the esters of acrylic acid, chloracrylic acid ormethacrylic acid and the lower aliphatic alcohols having not over fourcarbon atoms, or mixtures of said esters, which are copolymerized witha. suitableamount of a vinyl or propenyl acrylate or chioracrylate ormethacrylate or mixtures thereof, and with or without other modityingsubstances. The hardness, strength, adhesion, resistance to heat,softening point and other physical characteristics or the bond aredetermined by the nature and the proportions oi the bond ingredients andthe method employed for making the article. By varying the amount of thecross linking agent, the strength and other physical characteristics ofthe bond may vary from approximately those of the linear chain ester tothose of the cross linking a ent. The grinding wheel structure, asdetermined by the volume percentages of the abrasive grains, bond andpores, is governed in part by the relative proportions of the bond andgrains used.

The base substance of the bond is made up primarily of an ester ofmethyl, ethyl, propyl or butyl alcohol and acrylic acid, chloracryllcacid or methacrylic acid. The properties of these various substances areexemplified in the fol-l lowing table:

Polymers oi methacmlic acid esters nn- Iso- Methyl Ethyl Propyl Butylbutyl Hardness (Piund), G at C 220 141 1 210 Tensile strength, lbs/sq.1m huntn gtiYfiu... 9000 5000 4000 1000 3400 p 5 ND stat), kgmnJcmJZi-1o. 5 7-.1 6.5 11.5 1.0

'methacrylate softens above 100 C. while n-butyl methacrylate is softand flexible at room tem- 2 asoaecc p flture- However, the branching ofthe alcowhich. ethyiidene diincthacrylate.

hol materially affects these various properties. methacrylaterapidlypolymer-ices at room tend as shown by the fact that isopropyl alcoholperature to form a hard, transparent, colorless forms a methacrylateresin that is almost resin having an index of refraction of 1.583. hardas is polymerized methyl methacrylate. This polymer is insoluble andinfusible.

Also, the isobutyl ester is much harder and has .By employing propyne ormethyl-acetylene a higher softening point and is less flexible than(lHsCECH in place of acetylene, I may make the straight chain butyiester. The tensile isopropenyl methacrylate. The other homostrength ofthe straight chain ester falls off as logues may be similarly preparedby using acrylic the molecular weight of the alcohol increases. 19 acidor chloracrylic acid instead of methacrylic Hence, these various estershave widely varying acid in the above defined procedure.

properties. 7 i may alternately prepare vinyl methacrylate When any ofthese base substances are co" as follows: polymerized with the vinyl orisopropenyl (a) By the addition of methacryi chlorid to acrylates,chloracrylates or methacrylates, it is acetaldehyde and subsequentlydehydrohalogenfound that the interpoly'mers have similarly ating theproduct.

variable characteristics depending upon the na- (b) By esterifyingethylene chlorohydrin with ture and the proportions of the ingredientssemethacryl chloride and dehydrohalogenating the lected. Hence, bysuitably choosing a linear chloroester thus formed.

chain type of ester as a base substance and mod-= These cross linkingmay he written in ifylng it with a suitable vinyl or lsopropenylesaccordance with the following formula? ter, I may make abrasive bondsof widely difler- I; 0 Y

ent properties.v 1 l H The linear chain types of esters may be ob NLHPOAgJFCflCHZ tained from suitable commercial sources or 5 m which Xmay be H, C1 and Y may be manufactured in agcordance with standard H orCH3. These variations in produce rteprocedure The vinyl or isoproponylcompounds spectively the acrylic, chloracrylic and methmay b made bymethods exem lified by the acrylic acid esters. If Y is H. the compoundsduction of inyl methaorylato which may be are the vinyl acrylates andmethacrylates, and prepared by the addition f acetylene to memo, if Y isCH3 this forms the isopropenyl acrylates crylic acid in the presence ofa mercuric sulfate and meihacrylaiesfl It will be appreciated thatcatalyst. One suitable procedure is as follows: each of these CompoundsContains two of the 111% Five grams of mercuric oxide are dissolved insaturated methylene P CH2: the groups one hundred cubic centimeters ofglacial acetic acid heated to a temperature of eighty-five to The lineartype 9f mommeflc alkyl ninety degrees centigrade with vigorous stirring.esters above defined may collolymefized with To this mixture is addedthree and three tenths the m cross linking agent desired cubiccentimeters (one per cent excess) of conprof/Drums Winch Preferablyrange from 05% centrated sulfuric acid mixed with five cubic cento about15% by Volume of the cross linking timeters oi glacial acetic .acid, andthis mixture 40 agent, with the balance formed 01 the alkyl ester isadded dropwise with stirring to the mercuric and h without OtherPolymerizable acotato solution, The mercuric ulf t is then polymerizablesubstances included therewith. A allowed to settle and the greater partof the resin made Wholly of the alkyl ester P Y- acetic acid drawn fl'by suction- Most cf the merized with an appreciable amount of the crosssulfuric acid is washed out of the catalyst by linking agent tends tohave a higher softening the addition of one hundred cubic centimeterspoint or a greater degree of infusibility and 1858 of glacial aoetioacid and drawing ofl n but flow under heat and to presentcharacteristics about twenty five cubic centimeters. which are moresuitable for grinding wheels than To this catalyst, one hundred cubiccentimeters has the line chain type ester- The hard" 0f one hunored pert th li acid mess on the Rockwell scale of 'methyl methtainingpyrogallol as a polymerization inhibitor EMT/15st? Varies fmm t0 and theaddition is added, and the mixture is heated to to thereto of 10% 0fVinyl methacrylate, for C. Acetylene gas, after passing through sulfuricample gives hardness between 55 f 59; acid, 1 added to t mixture at therate of about hence the variation in hardness is slight aleight l t perhoun The gases issuing fro t 55 though the other properties as abovediscussed reaction flask are passed through a trap cooled are materiallyimproved 7 in ice water which collects a considerable quan- Thesestances are preferab y interpolymentity 01 vinyl methacry1ate t the endf 5 iced in such compatible amounts wherein the or eight hours, thecatalyst is filtered on and mimmnelic q s are fully b e d e the filtrateis combined with the liquid from the so polymerized product is ahomesenous. substant other and the tiaily one phase mass. For example, Imay co- @ueous sodium polymerize from 1 to 15% by volume of vinyl L 6other methacrylate with methyl methacrylate, by heatide, it di t-sli g Iin without the addition of still off and are not 1 s .02% of henits.such as .rty millimeters. The next product collected ethylidenediniethacrylete which boils at so eleven millimeters pressure. Con

.y changed to give a greater yield of vinyl iiiethacrylate by increasingthe rate or" flow of acetylene and condensing the vinyl rnethacrylate inthe trap outside the reaction mix ture, thereby hindering the secondaryreaction made the methacrylate and amount of ben grams oi this mixtureis poured with 1656 grams of abrasive grains into an aluminum orstainless steel mold shaped to form a grinding wheel. The abrasivegrains may be of any desired type, such as aluminum oxide or siliconcarbide, and of any suitable grit size. The liquid quickly penetratesinto the mass of abrasive grains, and wets them all but having aspecific gravity less than the grains there will be a clear liquid abovethem. The mold is heated in an oven to 60 C. for a period of about 24hours. The wheel may then be given a final bake at 110 C. for a periodof hours. Thereafter, the wheel is removed from the mold, bushed andtrued as desired. The times and temperatures given are illustrative andmay be varied widely with good results, those given being recommended.

For the manufacture of other types of grinding wheels I may producefirst a solid interpolymer of the selected ingredients and mix theabrasive grains and the dry resin powder with a suitable plasticitydeveloping medium, such as methacrylic acid, and shape a. grinding wheeltherefrom and thereafter complete the article by a suitable heattreatment. The bonding powder may be made as follows: To 33 c.c. ofvinyl methacrylate and 570 c.c. of methyl methacrylate is addedsix-tenths of a gram of benzoyl peroxide. The mixture is then added to1400 c.c. of carbon tetrachloride, in which it is completely miscible,and placed in a constant temperature bath maintained at 65 C. After aninduction period of about flve hours the copolymer, being insoluble inthe carbon tetra chloride, begins to precipitate as a fine powder and isfiltered on, washed with carbon tetrachloride and dried. I may alsopolymerize the mixture of vinyl methacrylate with methyl methacrylate toa massive piece and then crush and grind it to form a powder. I mix 1656grams of abrasive grain with 500 grams of the above described powder andplace in a mold. The mixture is pressed for thirty minutes in ahydraulic press with platens heated to 160 C. The wheel is thencomplete, the heat and pressurehaving softened and coalesced the resin,so that it forms with the abrasive grains an integral piece.

Other methods of procedure, such as set forth in the Kistler and Barnesapplication Serial No. 228,004 filed Sept. 1, 1938, of which I am one ofthe co-applicants, may be employed for producing suitable types ofabrasive articles. For example, methyl methacrylate or other chosenlinear chain type of alkyl ester and one of the cross linking agents maybe mixed in desired proportions, such as 90-parts of the base substanceand of the cross linking agent, and this monomeric mass, together with0.02% of benzoyl peroxide or other catalyzer may be heated to 80 C. forabout 1 hour. This viscous liquid is then mixed with the abrasive'grainsand the mass shaped as desired after which polymerization is completed.The plastic mass of abrasive grains and the partially polymerized bondmay be shaped in a suitable mold and preferably with pressure requiredto give the desired structure. A shaped mass is thereafter heated,either within or outside of the mold, to complete the polymerization ofthe bond. This step may comprise heating the molded mass in an oven at60 C., with or without the aid of light, for 24 hours to substantiallycomplete the polymerization of the monomeric substance presout; afterwhich it, may be given a further final baking treatment at C. or higherfor a period of 5 hours or so. The temperature time conditions may bewidely varied.

The porosity of the article depends upon the relative proportions of theabrasive grains and the bond, and the procedure set forth in thepatentto Howe and Martin No. 1,983,032 may be adopted in order to make acontrolled volume structure. The percentage by weight of the bond in agrinding wheel'may vary from 4 or 5% by weight for a very soft wheel to30% or more for a harder wheel.

. It will now be appreciated that the characteristics of the abrasivearticle will vary widely in accordance with the materials andproportions selected. For example, methyl methacrylate softens in theneighborhood of 100 C. depending upon the method employed for measuringthe same and 10% of vinyl methacrylate interpolymerized therewith givesa softening point of C. when similarly measured. The vinyl andisopropenyl acrylates provide somewhat softer bodies and have a lowersoftening point, but nevertheless these substances are useful as crosslinking agents. For example, a bond of methyl methacrylate used alonewill smear over the face of a grinding wheel in a dry grindingoperation. An interpolymer of that ester with 15% of vinyl acrylate, forexample, softens at a lower point. but this interpolymer will not smearand thus is greatly superior in that characteristic. This results fromthe fact that an increase in the amount of vinyl or isopropenyl esterdecreases the ability of the interpolymerized material to fiow underheat. Hence, the interpolymer which is even softer than methylmethacrylate may be superior for certain types of abrading operations.

It is also to be understood that I may utilize other polymerizablesubstances in connection with the ones above discussed for the purposeof imparting other desired properties to the bond; and such othersubstances may be incorporated in the bond without departing from thespirit and the scope of this invention; hence the claims are to beinterpreted accordingly as not excluding the presence of such othersubstances. The above disclosure is therefore to be considered asillustrating the general principles of my invention and preferredembodiments and compositions thereof and not as imposimr, limitations onthe claims appended hereto.

This case is a continuation in part of my prior application Serial No.227,108 filed Aug. 2'7, 1938.

I claim:

1. An abrasive article comprising abrasive grains united by a bondcomposed primarily of a resin formed of copolymerized substancescomprising an ester of an alkyl alcohol having not over four carbonatoms per molecule and an acid selected from the group consisting of theacrylic, chloracryllc and methacrylic acids copolymerized with an esterselected from the group consisting of the vinyl and isopropenyl estersof one of said acids.

2. An abrasive article comprising abrasive grains united by a bondcomposed primarily of a resin formed of copolymerized substancescomprising an ester 0i an alkyl alcohol having not over four carbonatoms per molecule and an acid selected from the group consisting of theacrylic, chloracrylic and methacrylic acids copolymerized with acompatible and miscible amount of an ester selected from the groupconsisting of the vinyl and isopropenyl esters of one of said acids,said allcvl ester constituting the major portion of the mass and thebond being a substantially homogenous one phase substance.

3. An abrasive article comprising abrasive grains united by a bondcomposed piimarily of a resin formed of copolymerized substancescomprising an ester of an allryl alcohol having not over four carbonatoms per molecule and an acid selected from the group consisting of theacrylic, chloracrylic and methacrylio acids copolyinerized in thepresence of the abrasive grains with from 0.5 to 15% of an esterselected from the group consisting of the vinyl and isopropenyl estersof one of said acids, said alkyl ester constituting the major portion ofthe mass and the bond being a substantially homogenous one phasesubstance.

4. An abrasive article comprising abrasive grains bonded as a porousintegral body by a lesser amount of a bond composed primarily of a resinformed of copolymerized substances comprising an ester of an alkylalcohol having not over four carbon atoms per molecule and an acidselected from the group consisting of the acrylic, chloracrylic andmethacrylic acids copolymerized with not over 15% of a compatible andmiscible amount of an ester selected 'from the group consisting of thevinyl and isopropenyl esters of one of said acids.

5. An abrasive article comprising abrasive grains bonded primarily by aresin formed of cm polymerized substances comprising an ester of an acidselected from the group consisting of the acrylic, chloracrylic andmethacrylic acids and an alkyl alcohol having not over four carbon atomsper molecule and branched as much as possible, which isinterpolyrnerized with a lesser compatible and miscible amount of anester selected from the group consisting of the vinyl. and isopropenyiesters of one of said acids.

6. An abrasive article comprising abrasive graii'is bonded prir ily by aresin formed of copolymeriaed subs rxcs comprising an ester or an. acidselected from the group consisting of the acrylic, chloracryig: andmethacrylic acids and an alkyl alcohol having not over four carbon atomsper molecule and less than a maximum branching which is interpclymerizedwith a lesser compatible and miscible amount of an ester selected fromthe group consisting of the vinyl and isopropenyl esters of one of said,acids.

'3'. An abrasive article comprising abrasive grains bonded. primarily bya resin formed methyl methacrylate copolymerized with an ester selectedfrom the group consisting of the vinyl and isopropenyl acrylates,chloracrylates and methacrylates.

8. An abrasive article comprising abrasive grains bonded primarily by aresin iormed of methyl methacrylate copolymerized with from 015 to 15%by weight of vinyl methacryla .c.

9. An abrasive article comprising abrasive grains bonded primarily by aresin formed of methyl methacrylate copolymerized with from 0.5 to 15%by weight of isopropenyl methacrylate.

10. An abrasive article comprising abrasive I grains bonded primarily bya. resin formed of methyl methacrylate copolymerized with from 0.5 to15% by weight of vinyl acrylate.

CARL E. BARNES.

